#include <fstream>

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
long n,d[5000002],v[5000002],i,j,p,u,k;
long long sol;
int main(){
    fin>>n>>k>>v[1];
    p=1;
    u=1;
    d[p]=1;
    for(i=2;i<=n;i++){
        fin>>v[i];
        while(p<=u && v[i]<=v[d[u]])
            u--;
        d[++u]=i;
        if(i-d[p]==k)
            p++;
        if(i>=k)
            sol+=v[d[p]];
    }
    fout<<sol;
    fin.close();fout.close();
    return 0;
}